Recently, mobile communication including portable telephone is developing from communication by voice into communication by data such as characters and moving pictures. Accordingly, an antenna for receiving radio waves is also required to be higher in performance.
A conventional antenna will be described with reference to FIG. 7 and FIG. 8.
FIG. 7 and FIG. 8 are schematic diagrams of conventional antennas, and the one shown in FIG. 7 is first described.
In the conventional one shown in FIG. 7, first wireless circuit 107 is connected to one end of first transmission line 105 disposed above ground plane 109. First feeder portion 103 is connected to the other end of first transmission line 105. And, first antenna element 101 is connected to first feeder portion 103. First antenna element 101 is extended to the top side of ground plane 109.
Further, similarly, second wireless circuit 108 is connected to one end of second transmission line 106 disposed above ground plane 109. Also, second feeder portion 104 is connected to the other end of second transmission line 106. And, second antenna element 102 is connected to second feeder portion 104. Second antenna element 102 is also extended to the top side of ground plane 109.
In the above configuration, first antenna element 101 resonates with the radio waves of the first frequency. In the receiving mode, current excited by radio wave received by first antenna element 101 is transferred from first feeder portion 103 to first wireless circuit 107 via first transmission line 105, and thereby, the radio wave are received.
On the other hand, in the transmitting mode, signal generated in first wireless circuit 107 is transferred from first transmission line 105 via first feeder portion 103 and is excited by first antenna element 101 to be emitted as radio waves and transmitted.
And, second antenna element 102 resonates with the radio waves of the second frequency, which is able to transmitted and receive radio wave on the same principle as for first antenna element 101.
Thus, as the setting is such that first antenna element 101 and second antenna element 102 respectively resonate with radio waves of different frequencies, the antenna shown in FIG. 7 is able to cope with two different communication systems.
And, in the conventional antenna shown in FIG. 8 that is different in configuration from FIG. 7, changeover switch 110 and changeover switch 111 are additionally inserted into first transmission line 105 and second transmission line 106 respectively.
The other components are same as those of FIG. 7, and the description is omitted.
In FIG. 8, when transmitting and receiving the radio waves of the first frequency, the antenna operates with changeover switch 10 turned ON and changeover switch 11 turned OFF. Also, when transmitting and receiving the radio waves of the second frequency, it operates with changeover switch 10 turned OFF and changeover switch 11 turned ON.
As prior art document information related to the present invention, for example, Japanese Patent Laid-Open Application No. S63-60628 can be mentioned.